浅谈汽车起重机回转系统设计

汽车起重机回转系统使用最频繁,作业时产生的压力冲击会影响相关液压元件工作寿命,制约回转系统的工作性能,所以如何减轻回转制动时的晃动是回转系统设计的核心。本文介绍了汽车起重机回转系统设计的要点,针对不同吨位的汽车起重机给出了一些设计方法。     

一种具有自适应节流的液压平衡阀设计及特性分析

为了提高液压平衡阀的控制精度,通过新增流量测试环节利用非线性阀口开口的方式来补偿流量产生增益,设计了一种具有自适应节流阀的液压平衡阀.该平衡阀能够根据不同工况条件适应负载变化的液压平衡阀遇到节流口流量变化时,同样会导致流量发生改变.研究结果表明:新平衡阀在不同流量下可以快速根据流量差异调节控制压力,从而防止因为流量差异...     

基于AMESim的破碎站输送带液压平衡回路的研究

该文针对破碎机输送带液压折叠时产生明显抖动爬行现象,分析了该系统可能出现故障现象的原因,并利用Amesim软件分析了输送带的液压平衡回路中平衡阀和油液含气量对系统稳定性的影响。结果表明：较小直径的平衡阀先导阻尼孔可以有效地提升系统的稳定性,减少油缸的振动爬行现象。但当平衡阀先导阻尼孔直径小到一定值以后再减小直径对系统稳定性的提升不再明显,且过小或过大的阻尼孔也容易引起较大的油缸启动速度波动。系统中液压油含气量越大,越不利于系统的稳定性。     

新型负载敏感平衡阀设计与装机试验

介绍了一种带折叠臂架的机械用新型负载敏感平衡阀,对其工作原理及结构特点进行了详细阐述.平衡阀芯采用节流孔组合的节流形式,借助MATLAB对节流口过流面积特性曲线进行拟合,当负载压力改变时,通过控制平衡阀芯位移,调节过流面积,达到稳定流量的目的.上述设计使得该阀不仅具有多级调节功能,而且负载敏感性得到提升.为了测试该阀在实际应用环境下的性能,在混凝土泵车上进行了装机试验.结果表明:该阀控制压力低,降低了系统功耗,负载敏感特性表现良好;臂架运行平稳,稳定性得到提升.     

管片拼装试验台回转电液控制系统设计及试验分析

 针对管片拼装机高速、高精度及低冲击自动拼装技术的需求,在全面分析了管片拼装机回转驱动系统大行程、大惯量及长时间运行特点的基础上,设计了以比例换向阀为调节核心、以平衡阀为辅助保障的管片拼装试验台回转电液控制系统.参考工程应用管片拼装机相关参数及管片拼装试验台设计要求,基于相似理论提出拼装试验台回转电液控制系统参数指标及原理图,运用SolidWorks建模仿真及负载力矩分析,进而完成电液控制系统参数设计及元件选型,最后完成了¢2 m管片拼装试验台回转电液控制系统的搭建及试验分析工作.试验分析结果表明：系统稳态性能满足设计要求,最大转速为6.25 r/min;同时具有良好的动态性能,系统阶跃响应峰值时间为1.1 s,可平稳实现斜坡减速及低速停车．     

节流槽结构参数对阀开启压力冲击及空化特性的影响研究

液压控制阀阀芯节流槽的结构对阀的动态特性影响强烈,不良节流槽结构将导致极大的液压阀开启瞬间压力冲击。针对某型号负载敏感多路阀在甘蔗联合收割机的应用中出现啸叫和液压冲击的问题,结合动网格与RNG-k-ε湍流模型,对U+T型节流槽和V型节流槽的压力冲击及空化进行了对比分析,发现同等条件下V型槽的阀芯较U+T型槽的阀芯的压力冲击下降了19.37%,最大空化程度降低了43.7%。选取V型节流槽开展进一步研究,通过正交试验获取不同节流槽结构参数下的压力峰值;采用BP神经网络建立V型节流槽结构参数与压力冲击的代理模型,结合灰狼优化(GWO)算法得到节流槽结构参数的最优配置;依据优化结果制作阀芯并进行试验,结果显示,抑制压力冲击效果显著,系统压力超调下降至原来52.4%。     

压力调节锥阀开启过程振动特性研究

压力调节锥阀开启调节过程的阀芯振动直接影响着系统的压力波动幅值和响应速度,通过实验获得了阀芯运动位移和系统压力波动曲线,研究了不同阀芯和阀体结构条件下锥阀开启过程的阀芯振动特性和系统激励因素。结果表明:压力调节锥阀开启调节过程中阀芯的振动状态与阀芯结构、流量及开启压力等因素密切相关;另外,在带阻尼孔的锥阀中,相同流量和压力条件下,球头阀芯较平头阀芯更容易出现超调振动现象;研究还发现,压力调节锥阀开启调节过程中阀芯的振动是由管路系统与模型锥阀的耦合共振引起的。     

小松PC130-7型挖掘机回转机构不能回转和上体回转角度偏大故障排除

针对小松PC130-7型挖掘机上体不能回转和上体回转角度偏大两种典型故障进行了分析,并提出了排除方法,对维修技术人员排除挖掘机回转机构液压系统故障具有一定的借鉴作用。     

基于自主气体轴承的大型光电精密仪器回转基准技术的研究

提出一种用于大型光电精密仪器的自主控制静压气体轴承方案。按气体轴承刚度最大准则优化了固有节流轴承参数。给出了进气、排气、进气-排气三种主动节流方式下的承载能力特性。计算结果表明,轴承参数优化是合理的,能为自主控制轴承实现无穷刚度提供良好的负载范围。三种主动节流方式也为自主控制气体轴承提供了多样性选择。     

基于Fluent的节流阀油液空化流场数值分析

基于计算流体动力学方法,数值研究了节流阀开度变化对节流阀内油液压力场、速度场及空化区域的影响。流道内压力较大区域位于上流道,压力较小区域位于下流道。节流口处压力梯度随阀口开度减小呈增大趋势;液压油低流速区分布在上游槽底部、阀芯顶端及阀腔拐角处。随着阀口开度减小,在通流截面积和油液黏性阻力共同作用下,通过节流口处流体流速呈先增大后减小趋势;在上游阀座底部、阀芯顶端处、阀腔拐角附近存在三个回流区,该回流区面积随阀口开度减小而减小;由于节流口处气体体积分数较高,因此空化初始位置位于节流口阀座附近,下游空化区则是游离性气泡群造成的。此外,随着开度进一步减小,空化强度呈先增强后减弱趋势,空化区域也呈先扩大后缩小趋势。     

液压滑阀阀芯结构对流场的影响

目的滑阀结构对阀流场有直接影响,为提高滑阀性能,对不同阀芯结构阀流场进行分析。方法采用U型、三角型和无节流槽3种阀芯结构,利用ADINA软件流固耦合模块,对3种阀芯的滑阀流场情况进行分析计算,研究阀流道内流体流速和压力分布情况。结果在进口处具有较高的流速,无节流槽阀芯在阀口处速度降低最大,U型节流槽阀芯在阀口处速度降低最小;U型节流槽阀芯在整个流道内压力变化较小,无节流槽阀芯在整个流道内压力变化最大。结论阀芯开设节流槽可以明显改善阀流道内流场分布情况,改善阀的性能,其中U型节流槽阀芯具有良好的性能。     

Fluid-dynamic design optimization of hydraulic proportional directional valves

This article proposes an effective methodology for the fluid-dynamic design optimization of the sliding spool of a hydraulic proportional directional valve: the goal is the minimization of the flow force at a prescribed flow rate, so as to reduce the required opening force while keeping the operation features unchanged. A full three-dimensional model of the flow field within the valve is employed to accurately predict the flow force acting on the spool. A theoretical analysis, based on both the axial momentum equation and flow simulations, is conducted to define the design parameters, which need to be properly selected in order to reduce the flow force without significantly affecting the flow rate. A genetic algorithm, coupled with a computational fluid dynamics flow solver, is employed to minimize the flow force acting on the valve spool at the maximum opening. A comparison with a typical single-objective optimization algorithm is performed to evaluate performance and effectiveness of the employed genetic algorithm. The optimized spool develops a maximum flow force which is smaller than that produced by the commercially available valve, mainly due to some major modifications occurring in the discharge section. Reducing the flow force and thus the electromagnetic force exerted by the solenoid actuators allows the operational range of direct (single-stage) driven valves to be enlarged.     

二通插装阀方向元件的动作响应特性研究

针对某造型机中二通插装阀方向元件的启闭特性,建立数学模型理论,分析插装阀阀芯动作特性的影响因素;利用AMESim建立二通插装阀模型,通过仿真分析弹簧刚度与预压缩力、阀芯面积比与油液通流方向、阻尼孔通径与安装位置等因素对阀芯动作特性的影响.由仿真结果可知:与弹簧预压缩力相比,阀芯的弹簧刚度对响应特性影响较大;油液在插装阀...     

主给水调节阀节流窗口周向设计及其对流动特性的影响

安装于核电站二回路的主给水调节阀通过控制给水流量来调节蒸汽发生器内的水位高度,因此主给水调节阀的流动特性影响着核电站的运行安全与效率.首先,提出了无量纲的节流窗口周向布置不平衡度δ,进行主给水调节阀节流窗口周向设计;其次,利用经网格无关性与流量实验验证的数值模拟方法分析了阀内流场的速度和压力分布特性;最后,探讨了节流窗...     

Instability of automotive air conditioning system with a variable displacement compressor. Part 2. Numerical simulation

A test system is built first in order to investigate the instability of the automotive air conditioning (AAC) system with a variable displacement compressor (VDC), and hunting phenomena caused by the large external disturbance in the AAC system with a VDC and a thermal expansion valve, and in the AAC system with a VDC and a fixed-area throttling device are investigated experimentally in part 1 of this paper. The experimental results indicate that there also exist the hunting phenomena in the AAC system with a fixed-area throttling device. The system stability is found to be dependent on the direction of the external disturbance, and the system is apt to cause hunting when the condensing pressure decreases excessively since it may cause two-phase state at the throttling device inlet and make a large disturbance to the system. The piston stroke length will oscillate only when the oscillation amplitudes of forces acting on the wobble plate are great enough, otherwise the piston stroke length will be kept invariable, and then the system instability rule is also suitable for the AAC system with a fixed displacement compressor. From the experimental results, it is concluded that the two-phase flow at the throttling device inlet or at the evaporator outlet is the necessary condition but not sufficient condition for system hunting. Finally, a new concept, conservative stable region, is proposed based on the experimental results and theoretical analysis.     

注水系统三级节流降噪设计及数值分析

大压差工况下,流量调节阀的节流作用导致自流注水系统振动噪声问题突出。为控制自流注水系统的噪声,从系统配置的角度进行系统降噪优化设计,提出了多级节流的降噪方案。采用流体动力学数值方法进行了多级节流低噪声设计原理分析,验证了多级节流降噪方案的有效性。基于低噪声设计原理,设计了三级流量调节阀串联的节流注水方案,并对三级节流系统进行了流场数值分析,数值分析结果表明:三级节流设计使各级阀后低压区减小,避免了阀后局部气蚀出现;一级阀门和二级阀门进口下缘及出口上缘均出现大尺度的漩涡结构,为主要噪声源区域。     

Experimental and simulation study of the effect of gravity on the solid-liquid two-phase flow and erosion of ball valve

The ball valve is an important control component in the pipeline hydraulic transmission system. Its internal solid-liquid two-phase flow and erosion characteristics have an important effect on the safety and stability of the entire pipeline system. Therefore, the erosion characteristics and positions of the ball valve body, the spool flow channel, and the pipeline surface behind the valve should be accurately predicted to ensure the safety of the pipeline. In this study, the experimental setup of the ball valve was designed. The experimental study on the erosion caused by the solid-liquid two-phase flow on the inner surface of the ball valve was conducted. And the numerical calculation research based on the CFD-DEM simulation method was performed. Results show that the placement of the ball valve has a great effect on the two-phase flow and erosion distribution inside the valve; the surface of the erosion plate will form a corrugated texture under the impact of particles at small openings; the placement method changes from vertical to horizontal due to the change in the direction of gravity. As a result, the particle distribution easily gathers near some wall surfaces to form a protective layer, which reduces the erosion rate.     

四通电磁换向阀液击损坏的预防措施分析

针对四通电磁换向阀(简称"四通阀")液击损坏问题,分析其液动力模型,发现避免四通阀换向时有液体流过、延长四通阀动作时间、减少阀口开度变化及阀口前后压差、增大阀芯材料强度等均可减少四通阀液击损坏。同时,采用楔形螺纹或预涂胶螺钉可以提高四通阀活塞与支架连接的可靠性;合理设置四通阀中间流量能够降低换向过程中的压力峰值。     

Investigation on failure process and structural optimization of a high pressure letdown valve

High pressure letdown valve in direct coal liquefaction is used to adjust the flow rate of coal–oil slurry that enters into the downstream separator. Severe erosion–cavitation wear is found on the valve spool, seriously affecting the safety and reliability of unit. The majority of this paper investigates the failure process of valve spool and proposes a corresponding structural optimization via computational fluid dynamics (CFD) methodology. Three geometries of different failure states are selected as the computational domains in the numerical simulation. The Schneer–Sauer model, particle rebound-velocity model and erosion model are employed to calculate the cavitation phenomenon and erosion rates distribution. Experiments of flow rates and cavitation on valve model under different pressure drops are conducted to validate the accuracy of numerical approach. Results showed that the damage development of valve spool aggravates the erosion–cavitation wear. The maximum erosion rates are located on the top of spool head in all the three states. The erosion rates on spool arc surface are two orders of magnitude higher than that on parabolic surface. The decrease in radius of spool head reduces the intensities of erosion–cavitation wear. The numerical results are in agreement with actual failure morphologies of valve spool in different states.